二分查找

二分查找的前提

1. 目标函数单调递增或递减
2. 存在上下界 bounded

3. 能够通过索引访问 index accessiable

   代码模板

   public int binarySearch(int[] array, int target) {
    int left = 0, right = array.length - 1, mid;
    while (left <= right) {
        mid = (right - left) / 2 + left;
        if (array[mid] == target) {
            return mid;
        } else if (array[mid] > target) {
            right = mid - 1;
        } else {
            left = mid + 1;
        }
    }
    return -1;
   }